In a semiconductor memory apparatus, a plurality of memory cells are arranged in a memory cell array, and each memory cell is connected to a first word line and a second word line, so that the hold currents are supplied from the word lines to the memory cells. In the memory cell array mentioned above, the word lines have an electrical resistance. Thus, the hold currents which are supplied to the memory cells are not uniformly distributed because the potential drop caused in the word lines decreases the noise immunity of the semiconductor memory apparatus. When the word lines are formed of a material having a high electrical resistance, such as poly silicon, the above-mentioned inconvenience appears. Furthermore, even if the word lines are formed of a metal, such as aluminium, when the memory apparatus is formed as a fine construction by a high integration technique, the above-mentioned drawback is magnified due to a parasitic resistance in the word lines.
The decrease in the noise immunity due to the non-uniform distribution of the hold current can be overcome by increasing the minimum hold current, thus improving the noise immunity in the memory cell having the minimum hold current. However, when the minimum hold current increases, the hold current in the other cells also increases, and therefore, the electric power dissipation in the whole memory apparatus increases.